50 
mr. j. c. Mclennan on electrical conductivity in gases 
10. Ionization in a gas independent of its chemical composition. 
11. Comparison of ionizations produced by cathode and by liontgen rays. 
12. Summary of results. 
1. Form of Tube adopted for the production of Cathode Fays. 
To produce the rays, a modified form of the tube devised by Lenard,* fig. 1, was 
used. The disc a which closed the end and carried the aluminium window formed 
the anode. To hold this disc in position, and to render the joint airtight, recourse 
was had to sealing-wax, which was allowed to set on the previously warmed glass and 
metal, after which the parts were made to unite by slightly melting the surfaces and 
pressing them together. By running round the joint with the pointed flame of a 
blowpipe, any air bubbles present were removed, and complete union was effected. 
Joints made in this way were found to hold for any time desired. 
In making the aluminium window airtight, marine glue could be used, but the 
ordinary commercial soft wax was found to be more suitable. This was especially so 
when the experiments were in the tentative state and alterations were frequently 
necessary. The wax melted at a lower temperature than the glue, and besides being 
much more manageable than the latter, it was also less disagreeable to handle. A 
coating of it on the sealing wax also prevented cracking. 
As shown in the figure, the anode was provided with a shoulder round the opening 
of the window. This was found very convenient when the action of the rays on the 
t/ t/ 
air in a partially exhausted receiver such as A was being examined. The receiver 
was provided with a similar but larger shoulder, and by slipping it over that on the 
* ‘Wied. Ann.,’ vol. 51, p. 225 (1894). 
